In an AC rotary machine having a plurality of windings, a plurality of current control systems interfere with each other due to mutual inductance between the plurality of windings, and therefore a current and a voltage are likely to become oscillatory, making it more difficult to widen a response band of the control systems than when a single system is used. Several methods have been proposed in response to this problem.
In one of these methods, employed in a conventional control apparatus for an AC rotary machine, a feedback signal transmitted from a plurality of inverters connected in parallel to a multiphase AC motor to a representative current control system provided on a rotary coordinate system of the AC motor is set at an average value of output currents from the respective inverters. Further, a feedback signal transmitted to an imbalance suppressing current control system provided on the rotary coordinate system of the AC motor is set at a differential value of the output currents from the respective inverters.
As a result, the imbalance suppressing current control system acts to equalize the output currents from the respective inverters, and therefore respective currents of windings of respective phases in the multiphase AC motor can be balanced.
Further, an unbalanced current can be reduced in a similar manner by the action of the current control system likewise in inverters that are connected in parallel using an external reactor.
By balancing the output currents of the respective inverters in this manner, the external reactor can be reduced in size or omitted, and control exhibiting high responsiveness can be realized (PTL 1, for example).
Furthermore, in a conventional control apparatus for an AC rotary machine, a non-interference voltage calculation unit is provided for each of respective control circuits of inverters INV1 to INVN that drive respective windings of a three-phase, N-layer winding motor, and an excitation command value IO*, a torque command value IT*, d, q axis current command values i1d*, i1q* obtained by dividing IO* and IT* by a number N of turns in the multiplex winding, and a primary side frequency ω are taken therein. d, q axis voltage set values v1d*, v1q* are then calculated from these values, whereupon non-interference control of the three-phase multiplex winding motor is realized by performing vector control (PTL 2, for example).